Geoheat for Greenhouses

We have developed a tool which can provide the basic subsurface data at a site of interest. By clicking on a location in the Auckland, Waikato or Bay of Plenty region, the geology, known temperatures, flow rates and aquifer details are displayed in a pop-out window.

Additionally, a financial indicator tool has been developed. On the right-hand side of the web page, you can insert details of your greenhouse (size, operating indoor temperature, humidity control, thermal screens, electricity and gas costs). By providing this basic information, the calculator will combine known subsurface information and operational information to provide simplified economic comparisons of geoheat options with gas boilers and air source heat pumps.

The assessments include basic ground loop design assumptions based on geological conditions and the heating demand. This allows a construction and set-up cost (CAPEX) for heating equipment to be estimated. OPEX costs are also calculated.

Check out the tool here(external link)

Assumptions and Design Choices for Greenhouse models

Heating options: Capital costs for installing a new gas boiler, air source heat pump (ASHP), ground source heat pump (GSHP), and geothermal direct use system are compared delivering the same heating requirements for each thermal envelope scenario. 

Greenhouse type: This model assumes a new build greenhouse, with different thermal envelope scenarios to demonstrate the impact that thermal efficiency has on operational energy cost (shown in figure above). 

Standard envelope → higher heat losses, reducing system efficiency. (4mm toughened diffused glass)

Improved envelope → improved efficiency; requires additional investment which has been included in the LCOH analysis (approx. 30% additional capital investment per m²). (Polycarbonate 16mm (White) U-Value 2.27 SHGC 0.66)

Size: input by users

Internal set point: input by users

Energy demand: Estimated from climate models for the location of choice, size of facility, and internal set point temperature.

Fuel costs: option for user to input Gas and Electricity costs. Below values are source in July 2025, from horticulture industry average. 

• LPG Gas Cost:                   0.275/ kWhr  
• Electricity Cost:                $0.319/ kWhr  
• Energy Inflation:              5 % per annum
• Carbon tax:                       NZD $64 per tonne CO₂-e 

Plant Operation: 24/7 heating availability

Analysis period: 25 years

Replacement:    ASHP 15 years, GSHP and boilers typically every 25 years. Geothermal direct use equipment will not need a replacement in a 25 year period.

Electrical Supply Considerations: cost for electrical supply equipment (e.g. transformers) has been excluded in this analysis for the GSHP and ASHP options. Lower electrical demand for a GSHP reduces required upgrade scale and can mean an upgrade may be avoided entirely where spare capacity exists. Upgrade costs can be significant and impact the business case for the electric options, however, they can only be determined on a case-by-case basis. 

Open or closed loop system: An assessment of the groundwater aquifer size and flow rate determines the number of wells needed for an open loop system.  If no or very low groundwater resource, a closed loop system could be considered but this option has not been considered in the calculations.

Well Design: for geothermal open loop designs, more reinjection wells than abstraction wells are required. This ensures that recharge to the aquifer is sustainable.

Geothermal Source Temperatures

Indirect use @ 20 °C → a ground source heat pump boosts the source temperature to between 60 and 80 C, to sustain an internal set point of 18°C.  

Direct use @ 50 °C → reflects international practice of targeting source temperatures of 40–45 °C. These lower source temperatures require increased internal pipe surface area to sustain 18C set point temperature. Alternative is to boost source temperature with gas backup, biomass, waste oil, ASHP, or GSHP. These options were excluded to simplify this analysis.

Direct use @ 70 °C → simple pipe network distributes high heat across the facility to maintain set point of 18°C. These temperatures reflect the operating source temperature commonly provided by gas or coal boilers.